Spray the bottom of a 9" pie plate with nonstick cooking spray. In a large bowl cream the butter until smooth. Add the flour, powdered sugar, and salt. Mix until combined and a soft dough is formed, the mixture will be crumbly, don’t over mix. Using your hands, press the crumbly dough into the prepared 9” pie plate.
Chill in the fridge for 20-25 minutes, or the freezer for 15 minutes. While the crust is chilling preheat the oven to 350°F. (At this time you can begin to make the sour cream pie filling if you'd like). Remove the crust from the fridge/freezer and bake for 15-20 minutes or until lightly golden. Allow the crust to cool completely before filling.
Make the Lemon Sour Cream Filling
Add the sugar, cornstarch, butter, lemon zest, lemon juice, egg yolks, and milk to a medium saucepan. Cook over medium heat, whisking frequently, until thickened. Remove from heat and pour the mixture through a fine mesh sieve. Cool completely.
Once cool, fold in 1 cup sour cream.
Pour the lemon sour cream mixture into a 9” cooked shortbread pie shell.
Place in the refrigerator to chill for at least 2 hours. Store pie covered in the fridge for up to 4 days. (Yes, this pie still tastes amazing several days later… as long you bake it in my shortbread pie crust, which holds up very well!)
Notes
Store leftover lemon sour cream pie tightly covered in the refrigerator for up to four days. Do not freeze.